Virtual reality can be viewed as a computer-generated simulated environment in which a user has an apparent physical presence. A virtual reality experience can be generated in 3D and viewed with a head-mounted display (HMD), such as glasses or other wearable display device that has near-eye display panels as lenses to display a virtual reality environment, which replaces the actual environment. Augmented reality, however, provides that a user can still see through the display lenses of the glasses or other wearable display device to view the surrounding environment, yet also see images of virtual objects that are generated for display and appear as a part of the environment. Augmented reality can include any type of input such as audio and haptic inputs, as well as virtual images, graphics, and video that enhances or augments the environment that a user experiences. As an emerging technology, there are many challenges and design constraints with augmented reality, from generation of the virtual objects and images so that they appear realistic in a real environment, to developing the optics small and precise enough for implementation with a wearable display device. There are also challenges to developing illumination sources for implementation as micro projectors and/or imaging units for wearable display devices.
Conventional LCOS (liquid crystal on silicon) projection technologies use an LED (light emitting diode) or laser source to generate light that is reflected off of a silicon transistor array covered by an LCD (liquid crystal display) material to either reflect and/or change the polarization of the light. The LCOS reflective technology uses liquid crystals instead of individual micro-mirror array MEMS (micro-electro-mechanical systems) mirrors. The liquid crystals are applied to a reflective mirror substrate and, as the liquid crystals open and close, the light is either reflected from the mirror below or blocked to modulate the emitted light. LCOS-based projectors typically use three LCOS chips, one each to modulate the red, green, and blue (RGB) components of the light. Similar to an LCD projector which uses three LCD panels, both LCOS and LCD projectors simultaneously project the red, green, and blue components of the light, such as for display on a display screen. A conventional display technology utilizes OLEDs (organic light emitting diodes) that generate light when current is applied through layers of the organic material. Although OLED cells can be individually controlled for illumination, unlike the LCOS material, the OLEDs are not viable for projection illumination because they do not emit enough light.
Some conventional LED array scanning systems for display technologies that have large optical systems are typically too large and complex to be implemented in imaging units for wearable display devices. Limitations of the current technology include the ability to modulate the emitters in sequence in a scanning system, which can result in a slow refresh rate, a blurred image quality, and/or limited color depth. Another limitation of conventional LED array scanning systems is the relatively larger pitch between the LED emitters, which results in a larger optical system with size and weight barriers to implementation in a consumer HMD product. The light that is emitted for LED array scanning is moved across a surface, such as via a MEMS mirror, LC scanner, or by moving optics. However, the light efficiency of each emitter can vary based on production and material variances, bonding issues, connectivity issues, driver variance, micro-optics, color conversion variance, temperature, and/or optic differences across the surface.
A number of correction techniques can be applied to drive each emitter with a correction curve to adjust for light efficiency variances. However, many of the correction curves are determined during manufacture and cannot be adjusted during use. Testing during production and manufacture can also be difficult and expensive because each emitter is tested at various emission points. Unlike conventional display devices, line and/or block scanning displays can exhibit display anomalies due to emitter light efficiency variances because any errors are also scanned over the display surface. For example, a single pixel failure in a conventional display may not be noticeable in a production device, whereas an error in a scanning device may result in an entire row of pixels being lost or displaying the incorrect light intensity level.